A comparison of observed upwelling mechanisms off the east coast of Australia

The East Australian Current (EAC) forms the western boundary current of the South Pacific sub-tropical gyre. Locally it plays an important role in the nutrient enrichment of the oligotrophic coastal waters of New South Wales (NSW), Australia. Observations from two detailed hydrographic surveys conducted during November 1998 and February 1999 are used to delineate the processes influencing nutrient enrichment across the continental shelf off the central east coast of Australia. Four nutrient enrichment mechanisms are identified: wind-driven upwelling, upwelling driven by the encroachment of the EAC onto the continental shelf, acceleration of the current resulting from the narrowing of the continental shelf at Smoky Cape, and the separation of the EAC from the coast. This study demonstrates that both the strength of the current and its proximity to the coast determine the nature of the upwelling response. An increase in nutrient concentrations occurs downstream as a result of each of the mechanisms identified. The highest nutrient concentration is attributable to the encroachment of the current onto the shelf, whilst separation induced upwelling is the most widespread.